Patent GB-538552-A (GB)
Title: Telephone systems
IPC: H04M1/278
Filed: 1939-09-29
Abstract: 538,552. Automatic exchange systems. STANDARD TELEPHONES & CABLES, Ltd. Sept. 29, 1939, No. 26874. Convention date, Sept. 30, 1938. [Class 40 (iv)] A subscriber's dial is replaced by an instrument which generates a selected two of a possible five frequencies for each digit, the five frequencies being different for each successive digit,. 'with the aid of reeds like those of a mouth organ and a microphone. All the digits are sent simultaneously. In both the instruments described the selection may be done in a single operation with the aid of previously prepared cards &c. for individual subscribers. At the exchange the musical signals are received by a register-controller which routes the call to a special operator if any of the composite signals corresponding to a digit comprises more or less than two of the possible five frequencies. Construction of sending devices. -In one arrangement, Fig. 6, the number is normally set up by adjusting strips 4, one for each digit, to bring a particular arrangement of two holes in each of the strips into register with two in each of a number of groups of five holes in a gasket 22 arranged at the upper ends of a number of air-conduits leading past a number of reeds 31 tuned to odd harmonies of 30 cycles to an air-chamber 24. Button 66 is then pressed and this (1) operates contact springs to give a signal at the exchange, (2) operates a device 54 for centring the strips 4 and (3) forces down a member 28 to which it is pivotally connected to draw air into bellows 27 and latches member 28 belowamember42. When the exchange is ready to record the number, a signal is sent back to energize a magnet 12 which closes a port in an air-chamber connecting the bellows to the air-conduits and removes the latch member 42. The rise of the button 66 then forces air from the bellows through the conduits selected by the strips 4 to vibrate certain of the reeds and the sounds from these affect a microphone button 33 in the air-chamber to signal the number to the exchange. In the case of frequently-wanted subscribers, the strips 4 are withdrawn to special positions and an individual strip is inserted between guide rollers 421. In a modified arrangement, Figs. 11 to 13 (not shown), masking discs controlled by knobs replace the strips 4. In this case also individual masking strips may be provided for frequently-wanted subscribers. Circuit arrangements. -The action of operating the button 66 loops the line through magnet 12 whereupon a finder F hunts for the line and a switch S1 hunts for an idle register controller. Magnet 12, being polarized, does not operate initially but 300, when the registercontroller is seized, pulls up over the loop and energizes 301 which reverses the connections of 300. Magnet 12 then pulls up and causes the transmission to line of a signal consisting of the combination of currents of different frequencies selected by the strips 4. The received signals are selected by filters and energize two relays in each group of five such as that shown at D. A normally-operated differential relay such as 390 associated with the receiving relays of a particular digit position is brought to the balanced condition provided that two and only two receiving relays are operated and when all the differential relays have dropped their armatures a circuit is made for 491 which provides the energizing battery for one in each of a number of groups of ten relays such as 368, 372 &c. This in turn energizes one or more of the relays in each of a corresponding number of five-relay registers such as 394, 369 &c. The register relays of each group lock in series with a group locking relay such as 370. If any of the receiving groups fails to receive a correct signal the failure of the corresponding differential relay to fall back prevents the operation of 491 and when 419, which pulls up sluggishly on the operation of 301, is operated, circuits are made for the top relays of all the groups of ten and these energize the first relays in all the five-relay registers to cause the call to be routed to an operator.